Digital readout instrument employing enablement circuits for system when under reading conditions

ABSTRACT

A digital readout thermometer employing a resistance bridge with a temperature sensitive element such as a thermistor in one leg of the bridge and including a motor driven adjustable resistance or potentiometer for rebalancing the bridge. A servo amplifier, d.c. motor and digital counter provide a reading indicative of the temperature. The circuit includes a differentiator for accelerating the time response of readout. It also includes timer, a comparator, logic circuit and visual indicator for enabling the readout system only when the transducer senses the temperature in the range to be read and the logic circuit is operative to enable the visual indicator when a temperature in the required range has been sensed for a period sufficient for the counter to complete its movement to the correct reading. The thermometer is automatically powered when the probe is removed from its storage tube.

United States Patent 1191 Brzezinski Jan. 15, 1974 DIGITAL READOUTINSTRUMENT Primary Examiner-Richard C. Q'ueisser EMPLOYING ENABLEMENTCIRCUITS Assistant Examiner-Frederick Shoon FOR SYSTEM WHEN UNDERREADING Attorney-John Wagner CONDITIONS [76] Inventor: JanuszBrzezinski, c/o John E. [57] ABSTRACT Wagner, 1041 E. Green St., Suite202 Pasadena Calif 91 106 A d1g1ta1 readout thermometer employing ares1stance bridge with a temperature sensitive element such as a 1Filed: June 28, 1971 thermistor in one leg of the bridge and including amotor driven adjustable resistance or potentiometer [*1] Appl' NO"157,465 for rebalancing the bridge. A servo amplifier, d.c. 1 motor anddigital counter provide a reading indicative [1.5. CI. of thetemperature The circuit includes a differenti- [51] Ill. CI. ator foraccelerating the time response of read0ut It of Search t also includestimer a comparator logic circuit and vi sual indicator for enabling thereadout system only 1 1 References Cited when the transducer senses thetemperature in the UNITED STATES PATENTS range to be read and the logiccircuit is operative to 3,702,070 11/1972 Georgi 73/362 AR enable theVisual indicator when a temperature in 346L734 3/1969 Tong 8t aim H73/362 AR required range has been sensed for a period sufficient3,550,448 12/1970 Ensign 73/362 AR x for he counter o complete i smovement to the cor- 3,360,993 l/l968 MacMillan 73/361 rect reading. Thethermometer is automatically pow 3,604,266 /19 1 C il on 73/362 AR eredwhen the probe is removed from its storage tube. 3,477,292 11/1969Thornton 73/362 AR 1'4 Claims, 6 Drawing Figures DC REGULATO REGULATORPATENTED JAN 1 5 I974 SHEET 1 0F 2 COMPARATOR TIMER MOTOR LAMP GATE

SENSOR FIG. 5

DIGITAL READOUT INSTRUMENT EMPLOYING ENABLEMENT CIRCUITS FOR SYSTEM WHENUNDER READING CONDITIONS RELATED INVENTIONS This application is animprovement upon my invention described in co-pending application Ser.No. 135,338 filed Apr. 19, 1971 which in turn in a continuation in Partof my application 32,142 filed Apr. 27, 1970, and now abandoned.

BACKGROUND OF THE INVENTION In my above identified patent applications Ihave disclosed a digital readout thermometer designed for use inmeasuring the human temperature employing a transducer which is broughtinto contact with the portion of the body to be sensed, a bridge switchfor measuring the temperature with respect to a standard, and a digitalreadout device which is powered by a dc. motor under the control of adual dc. power supply. This electronic thermometer of my inventionprovides accuracy of measurement in the order of l/l; and far greatervthan is available using conventional glass thermometer. This improvedaccuracy, however, also results in a sensitive response of thethermometer under a slight change in temperature which can result inchange in contact of the probe with the body. Likewise with such anaccurate measuring device which is of a null seeking nature, thebalancing of the bridge at the null occurs at a final lower speed whichis sometimes termed as a creeping of the digital readout. As a result,this improved accuracy in the thermometer has produced some uncertaintyon the part of the user at the time to take a reading. An accuratereading can be obtained in approximately seconds but a slight creepingthereafter can occur and an over-zealous person taking a reading maytake a minute or more watching for additional movement of the digitalreadout. This longer period for reading also results in increase inbattery consumption and does not necessarily produce a more accuratereading.

Prior art electronic thermometers have not solved the problems ofresponse, creeping, unnecessary battery drain or the need for a visualindication of the correct time to read the thermometer.

BRIEF STATEMENT OF THE INVENTION Given the background on the invention,I have invented an improved electronic thermometer in which the digitalreadout system is inoperative until a temperature in excess of apredetermined level, for example, 94 is sensed by the probe. I have alsoincluded a timer means for timing the period after sensing a temperaturein excess of a predetermined level for enabling the digital readoutcircuit whereupon the electronic circuit is capable of advancing to thesensed reading. I have also discovered that it is possible using a logiccircuit and indicator to give a visual indication of the correct time toread the temperature.

Therefore, employing this invention, the user need only replace thetransducer in contact with the body to be sensed and watch for theindicator light to come on which may be in the matter of a few secondsand then remove the transducer. The digital readout device holds thereading.

I have also included in my invention a switch means which is actuatableby removal of the probe from the storage device for enabling thecircuit, thereby eliminating the need for any other manual switch andeliminating any excess current drain.

BRIEF DESCRIPTION OF THE DRAWINGS The following features of thisinvention may be more clearly understood from the following detaileddescription and by reference in the drawing to which:

FIG. 1 is a perspective view of an electronic thermometer in accordancewith this invention with portions broken away for clarity;

FIG. 2 is a fragmentary portion of the thermometer of this invention;

FIG. 3 is a block diagram of the improved circuit of this invention;

FIG. 4 is a graphical representation of the operation of this invention;

FIG. 5 is a block diagram of an alternate embodiment of this invention;and

FIG. 6 is an electrical schematic diagram of a logic circuit preferredfor use in the embodiment of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Now referrring to FIG. 1, anelectronic thermometer 10 in accordance with this invention may be seenas including a housing 11 of generally rectangular shape and design tobe hand carried or in a strap supported carrying case in the positionshown. The top surface includes a visual temperature indicator in theform of a digital readout device 12. The top surface also includes alamp 13 a probe receiver or tube 14 and a probe jack (unshown). Plug orconnector 15 is inserted in the probe jack to connect a probe 16 vialead 17 to the thermometer 10. The probe is an elongated plastic bodywith a temperature sensitive resistance element or thermistor 20imbedded in its tip.

The probe 16 is normally stored in its receiver 14 with the tip of theprobe extending nearly to the bottom of the housing 11. As is shown inthe cutaway portions of FIGS. 1 and 2, the side wall of the probe 16contacts a spring contact 21 of a switch 22 to maintain the switch 22open whenever the prob-e 16 is in its receiver 14. Switch 22 is the mainpower switch from the batteries of the device one of which battery 23appears in the drawing. Therefore all power for the circuit isinterrupted during storage of the probe and power is automaticallyapplied to the sensing circuit whenever the probe 16 is removed from itsreceiver 14. The front face of the housing 19 also includes a batterycondition meter 24 visible to the user.

In addition to the full automatic powering of the circuit via the switch22 of FIGS. 1 and 2, several other features of this invention arepresent in the circuitry as shown in FIG. 3. The basic double DC. powersupply, bridge and servo circuits are of the type disclosed in mycopending Continuation application referenced above and the details andoperation of the basic circuit thereof may be best understood byreference to that application. Suffice it to say, the circuit includes apair of batteries 23A and B series connected with a center tap systemground G and switch 22 for applying power from the batteries 23 torespective voltage regulators 25 and 26. A battery condition meter 24 isconnected accross opposite poles of batteries 23 in series with a zenerdiode 27. This zener diode 27 is selected with a zener or breakdownvoltage of approximately percent of the normal terminal voltage of thebatteries 23, e.g. a 14 volt zener for use with two 9 volt batteries.The meter will then read full scale for a normal full terminal voltageand zero for any terminal voltage of less than 14 volts. Thisarrangement presents a clear indication of a slight drop in'batteryterminal voltage to allow replacement before the accuracy of readings isaffected.

The voltage regulators and 26 as disclosed in my copending patentapplication referenced above are preferably zener regulators with RC lowpass filters to provide a dual polarity regulated voltage to thetemperature sensing circuit.

The basic sensor, probe 16 is connected in one leg of a resistancebridge 30. Two nodes of the bridge are connected to the regulated supplymeter 33. The leg of bridge 30 opposite the probe 16 is connected to adifferentiator, amplifier 34 which provides a voltage output which is afunction of the voltage and rate of change of voltage across the bridge.It typically is an amplifier with a parallel R.C. circuit at its input.The presence of differentiator amplifier 34 accelerates the response ofthe thermometer without affecting its accuracy of the reading. Thissignal is applied to the input of a servo amplifier 35 in the servocircuit of the thermometer. The output of amplifier 35 is a function ofthe bridge balancing voltage of potentiometer 33, signal fromdifferentiator amplifier 34 and motor current fed back through aresistance 36. The operation of the bridge and servo of this inventionwith the exception of the differentiator amplifier 35 and a switch andlogic circuitry 41 is identical with that of my copending patentapplication and reference is made thereto for the details of operation.Suffice it to say, that signals from differentiator amplifier 35 andbridge unbalance signals on the wiper 33a combined in amplifier 35 andpassed through switch 40 (when in conducting condition) to a currentamplifier 42 to drive motor 43. The motor 43 is mechanically coupled tothe digital readout 12 through a reduction gear 44. The motor 43 is alsocoupled through a gear train 45 to the wiper arm 33a to rebalance thepotentiometer 33 to reduce the output signal of amplifier 35 to zero.

The other novel features of this invention involve particularly thelogic circuitry 41. This circuitry employs basically a voltagecomparator a timer 51 and a gate 52 as well as switch 40.

The comparator 50 has a pair of input leads A and B. The lead A isconnected to the center tap between resistances 31 and 32 whereby thepotential of the input A is equivalent to a selected measuredtemperature, e.g. 94F. The lead B is connected to the output of thedifferentiator amplifier 34.

The output of the differentiator amplifier 34'is the differentiatedamplified output of the bridge 30. Therefore the output is a function ofthe temperature measured by the probe 16. This relationship may berepresented by the following equation:

where T is the temperature sensed by the probe 16 and dT/d'r is thederivative of temperature with respect to time.

As the bridge becomes balanced, the time rate factor approaches zero andthe input B represents the T factor alone, or in other words, representsthe Probe temperature.

The differentiation function allows the system to respond at a fasterrate in balancing the servo system than in the case of a measurementbased upon direct measurement of temperature alone. Of course, a directmeasurement of temperature as indicated by the bridge unbalance couldoptionally be used in accordance with conventional wheatstone bridgetechnology. However, the differientator-amplifier approach is preferred.The comparator 50 produces an output pulse whenever the voltage on leadB exceeds that of lead A, i.e., the probe temperature is above theselected temperature. This condition triggers timer 51 which may be aone shot multivibrator having a pulse length of several seconds,sufficient time for the probe temperature to approach the patientstemperature. Timer 51 enables switch 40, at the beginning of its timingcycle, allowing current to flow to the motor 43 to drive counter 12 andrebalance the potentiometer 33. After the potentiometer 33 is rebalancedand the counter 12 displays the sensed temperature and the timer 51pulse is passed, gate logic applies operating current to lamp 13indicating the time to read the patients temperature.

The logic circuit 41 providing these functions is shown in FIG. 6. Thecomparator 50 produces an output current through diode whenever B 2 Aand simultaneously starts timer 51. The output of timer 51 through diode61 and combination with a negative voltage supply 62 snd groundconnection 63 establish the base bias of a PNP transistor 64. Theemitter and collector of transistor 64 are connected in the lamp 13power circuit. As connected, the lamp 13 is powered through transistor64 whenever the base of the transistor 64 is negative biased by supply62. This occurs when comparator is in its on or 1 condition and timer isoff (0). Below is a truth table for the logic circuit 41.

Comparator Timer 5] Motor 43 Lamp B 2 A 0 0 l B 3 A l l 0 B A 0 0 0 Nowrefer to FIG. 4 where the curve of operation of the system areillustrated. The solid curved line denotes the temperature of the probesensor 20 of FIG. 1 upon insertion in the patients mouth starting fromambient temperature T The probe increases in a smooth temperature risecurve until removed from the patients mouth at temperature Tp whereuponit falls toward the ambient.

As illustrated by the dash dot line, the indicator had a previousreading of and remains at that reading until the servo circuitry isenabled. This occurs when the probe temperature exceeds a preselectedvalue, e.g., 94 shown by the intersection of the dashed and solid lines.At this instant the comparator 50 of FIG. of FIG. 3 produces an outputpulse of (1) condition starting both the timer 51 and motor 43 asdenoted by the (1) condition. After the timer passes its preselectedtime interval and return to an off (0) position, the motor likewise isdeenergized. Lamp 13 is enabled and remains illuminated as long as thecomparator is in its (1) condition.

The indicator follows the dash dot line as illustrated falling to meetthe rising probe temperature line, with a small undershoot and overshootand stabilizing after the period of the timer interval. The indicatorthen with motor current removed holds the same reading until a newreading is taken. No resetting is required.

Given the foregoing features of this invention, I have truly anautomatic thermometer with the sensing circuitry powered only when theprobe is removed from its storage position and with the servo circuitpowered only when temperatures above a selected value are sensed. Logiccircuitry lights a lamp when the above conditions have been met andsufficient time has passed to establish an accurate reading. Subsequentcreeping of the readout is prevented by the logic circuit which removespower from the servo circuit during and after the reading condition.

In the foregoing description, the electronic thermometer of thisinvention is totally portable and self powered. In certain applicationssuch as intensive care needs of hospitals, portability is not requiredand in fact a permanent installation for each patient is desired. Underthese circumstances, the circuit of FIG. 5 is preferred. It employs asensor or probe 80 connected to bridge 81, a differentiator andamplifier 82, comparator 84, timer 85 and gate 86 and indicator lamp 87all equivalent to the same components in the circuit of FIG. 3. In placeof the servo system of FIG. 3, in this embodiment a digital voltmeter 90provides the visual readout of temperature. The voltmeter 90 and lamp 87may be located at the patients bedside or at a central monitoringstation if desired. In any case, the system of FIG. 5 employs the samelogic of FIG. 3 and provides the same automatic operation and a visualtime to read signal. The system of FIG. 5 includes comparator 84connected to the bridge 81 and the differentiator amplifier 82 tocompare any bridge unbalance indicative of a temperature sensed bysensor 80 in excess of a selected value e.g. 95. Comparator 84 enablestimer 85 which may be a one shot multivibrator having an output pulse ofselected length, for example 6 seconds.

The timer 85 provides an enabling input to the digital voltmeter 90 tocause it to display the temperature signal appearing on lead 91. Thetimer 85 and comparator 84 also enable gate 86 after the time intervalthereupon lighting lamp 87. Therefore similar to the embodiment of FIG.3, the readout digital voltmeter 90 is enabled and the lamp 87illuminated during the period when a reading may be taken. In certaincases, digital voltmeters may be used which are dark when not enabledand illuminated when displaying a reading. When using such a display,the lamp 87 may be eliminated and the lead 88 instead connected as theenabling input to the digital voltmeter 90. In this case, the referencevoltage for the comparator is an independent reference voltage source incontrast with the embodiment of FIG. 3. In fixed installations such anindependent reference may be desired.

It is recognized that following the teaching of this invention, onecould, through minor changes within the scope of teaching, producevariations which carry out the substance of the invention while havingminor difference in detail. Therefore, the monopoly afforded by thispatent shall not be restricted to the foregoing specific embodiments butinstead by the invention as described in the following claims and theirequivalents.

I claim:

I. Electronic thermometer comprising:

a probe having temperature sensitive element therein,

an enclosure,

circuit means within said enclosure for determining temperature of thetemperature sensitive element of said probe;

said circuit means including sensing circuit and a servo followupcircuit,

a temperature display connected to be driven by said servo followupcircuit,

said enclosure including a recess for storing said probe when not inuse;

first switch means responsive to removal of said probe from said recessfor applying operating power to said sensing circuit; and

second switch means responsive: to operation of said first switch meansplus the sensing of a predetermined minimum temperature by said sensingcircuit for applying operating power to said servo followup circuit.

2. The combination in accordance with claim 1 including differentiatoramplifier means connected between said sensing circuit and said servocircuit for producing an output signal for driving said servo circuitrelated to the temperature and rate of change of temperature sensed saidprobe.

3. The combination in accordance with claim 1 wherein said meansresponsive to said temperatures above the preselected minimum comprisesa comparator amplifier including one input terminal connected to areference voltage source and a second input terminal connected to saidsensing circuit to produce a signal whenever the sensing circuit detectsa voltage above the reference voltage.

4. The combination in accordance with claim 3 including switch meansresponsive to the output of said comparator amplifier for enabling theservo circuit.

5. The combination in accordance with claim 4 including a timerresponsive to the output of said comparator for limiting the time ofenablement of said servo followup circuit to a period sufficient forsaid servo followup circuit to make the maximum followup adjustment.

6. An electronic thermometer comprising a probe including a temperaturesensitive element therein,

a sensing circuit for producing an electrical signal related to thetemperature sensed by said probe,

an indicator,

a servo circuit for driving said indicator to a reading indicative ofthe temperature sensed by said probe,

a reference signal source,

comparator means for comparing the electrical signal produced by saidsensing circuit with said reference signal and for enabling said servocircuit only when said former signal exceeds the reference sig nal, and

timer means for limiting the time of enablementof said servo circuit toa time sufficient to followup to the temperature sensed.

7. The combination in accordance with claim 6 wherein said timer isconnected to said comparator to be enabled by the signal from saidcomparator.

8. An electronic thermometer comprising:

a probe including a temperature sensitive element therein;

a sensing circuit for producing an electrical signal related to thetemperature sensed by said probe;

a temperature display;

a servo circuit for driving said temperature display to a readingindicative of the temperature sensed by said probe;

a reference signal source;

comparator means for comparing the electrical signal produced by saidsensing circuit with said reference signal and for enabling said servocircuit only when said former signal exceeds the reference signal;

timer means for limiting the time of enablement of said servo circuit toa time sufficient to followup to the temperature sensed; and

indicator means for producing a signal to the user of the beginning ofthe period of time during which said display registers the probetemperature.

9. The combination in accordance with claim 8 wherein said indicator isa lamp and including means for lighting said lamp following the enablingof said timer.

10. The combination in accordance with claim 9 including means forextinguishing said lamp whenever" said probe is at a temperature lessthan the said predetermined minimum.

12. The combination in accordance with claim 11 wherein said lampextinguishing means comprises said comparator.

13. The combination in accordance with claim 10 including gate meansresponsive to a signal from said comparator and the end of a timingperiod of said timer for illuminating said indicator.

14. The combination in accordance with claim 13 wherein said gateresponds to the absence of a signal from said comparator to extinguishsaid indicator.

1. Electronic thermometer comprising: a probe having temperaturesensitive element therein, an enclosure, circuit means within saidenclosure for determining temperature of the temperature sensitiveelement of said probe; said circuit means including sensing circuit anda servo followup circuit, a temperature display connected to be drivenby said servo followup circuit, said enclosure including a recess forstoring said probe when not in use; first switch means responsive toremoval of said probe from said recess for applying operating power tosaid sensing circuit; and second switch means responsive to operation ofsaid first switch means plus the sensing of a predetermined minimumtemperature by said sensing circuit for applying operating power to saidservo followup circuit.
 2. The combination in accordance with claim 1including differentiator amplifier means connected between said sensingcircuit and said servo circuit for producing an output signal fordriving said servo circuit related to the temperature and rate of changeof temperature sensed said probe.
 3. The combination in accordance withclaim 1 wherein said means responsive to said temperatures above thepreselected minimum comprises a comparator amplifier including one inputterminal connected to a reference voltage source and a second inputterminal connected to said sensing circuit to produce a signal wheneverthe sensing circuit detects a voltage above the reference voltage. 4.The combination in accordance with claim 3 including switch meansresponsive to the output of said comparator amplifier for enabling theservo circuit.
 5. The combination in accordance with claim 4 including atimer responsive to the output of said comparator for limiting the timeof enablement of said servo followup circuit to a period sufficient forsaid servo followup circuit to make the maximum followup adjustment. 6.An electronic thermometer comprising a probe including a temperaturesensitive element therein, a sensing circuit for producing an electricalsignal related to the temperature sensed by said probe, an indicator, aservo circuit for driving said indicator to a reading indicative of thetemperature sensed by said probe, a reference signal source, comparatormeans for comparing the electrical signal produced by said sensingcircuit with said reference signal and for enabling said servo circuitonly when said former signal exceeds the reference signal, and timermeans for limiting the time of enablement of said servo circuit to atime sufficient to followup to the temperature sensed.
 7. Thecombination in accordance with claim 6 wherein said timer is connectedto said comparator to be enabled by the signal from said comparator. 8.An electronic thermometer comprising: a probe including a temperaturesensitive element therein; a sensing circuit for producing an electricalsignal related to the temperature sensed by said probe; a temperaturedisplay; a servo circuit for driving said temperature display to areading indicative of the temperature sensed by said probe; a referencesignal source; comparator means for comparing the electrical signalproduced by said sensing circuit with said reference signal and forenabling said servo circuit only when said former signal exceeds thereference signal; timer means for limiting the time of enablement ofsaid servo circuit to a time sufficient to followup to the temperaturesensed; and indicator means for producing a signal to the user of thebeginning of the period of time during which said display registers theprobe temperature.
 9. The combination in accordance with claim 8 whereinsaid indicator is a lamp and including means for lighting said lampfollowing the enabling of said timer.
 10. The combination in accordancewith claim 9 including logic means for enabling said lamp responsive toan enabling signal from said comparator and after the termination ofsignal from said timer whereby said lamp is illuminated only after atemperature above a predetermined minimum is sensed and after thenecessary time for said servo followup system to move said indicator toa temperature reading equal to the temperature sensed by said probe. 11.The combination in accordance with claim 10 including means forextinguishing said lamp whenever said probe is at a temperature lessthan the said predetermined minimum.
 12. The combination in accordancewith claim 11 wherein said lamp extinguishing means comprises saidcomparator.
 13. The combination in accordance with claim 10 includinggate means responsive to a signal from said comparator and the end of atiming period of said timer for illuminating said indicator.
 14. Thecombination in accordance with claim 13 wherein said gate responds tothe absence of a signal from said comparator to extinguish saidindicator.